Due to urban planning，flood discharge，land acquisition，and other factors，it is difficult to select new river-crossing bridge routes for large mountainous rivers in urban areas. In addition，many buildings have been built across the river，and they have been built in different years，which thus forms river segments with complicated bridge groups，and each bridge has different technical standards for navigation. This paper uses a planar two-dimensional flow mathematical model to analyze in detail the hydrodynamic conditions and the range of effective navigable water area of the river segments with bridge groups for the bridge to be built. At the same time，through the ship control simulation test，the paper studies the arrangement of piers and the safety of ships sailing through the river segments with bridge groups after the bridge is built. The results show that after engineering measures are implemented，the navigable flow condition of the river segments in the bridge area is improved，and the ship collision probability for the bridge to be built is very small. Therefore，the navigable water area determined by the river segments with bridge groups is reasonable.